Other methods of lift

Other methods of lift

A lifting body is the opposite of a flying wing. In this configuration the aircraft body is shaped to produce lift. If there are any wings, they are too small to provide significant lift and are used only for stability and control. Lifting bodies are not efficient: they suffer from high drag, and must also travel at high speed to generate enough lift to fly. Many of the research prototypes, such as the Martin-Marietta X-24, which led up to the Space Shuttle were lifting bodies (though the shuttle itself is not), and some supersonic missiles obtain lift from the airflow over a tubular body.
Powered lift types rely on engine-derived lift for vertical takeoff and landing (VTOL). Most types transition to fixed-wing lift for horizontal flight. Classes of powered lift types include VTOL jet aircraft (such as the Harrier jump-jet) and tiltrotors (such as the V-22 Osprey), among others. A few examples rely entirely on engine thrust to provide lift throughout the flight. There are few practical applications. Experimental designs have been built for personal fan-lift hover platforms and jetpacks or for VTOL research (for example the flying bedstead).
The FanWing is a recent innovation and represents a completely new class of aircraft. This uses a fixed wing with a cylindrical fan mounted spanwise just above. As the fan spins, it creates an airflow backwards over the upper surface of the wing, creating lift. The fan wing is (2005) in development in the United Kingdom.

Rotorcraft

Rotorcraft

Rotorcraft, or rotary-wing aircraft, use a spinning rotor with aerofoil section blades (a rotary wing) to provide lift. Types include helicopters, autogyros and various hybrids such as gyrodynes and compound rotorcraft.
Helicopters have powered rotors. The rotor is driven (directly or indirectly) by an engine and pushes air downwards to create lift. By tilting the rotor forwards, the downwards flow is tilted backwards, producing thrust for forward flight.
Autogyros or gyroplanes have unpowered rotors, with a separate power plant to provide thrust. The rotor is tilted backwards. As the autogyro moves forward, air blows upwards through it, making it spin.(cf. Autorotation)

US-Recognition Manual (very likely copy of German drawing)
This spinning dramatically increases the speed of airflow over the rotor, to provide lift. Juan de la Cierva (a Spanish civil engineer) used the product name autogiro, and Bensen used gyrocopter. Rotor kites, such as the Focke Achgelis Fa 330 are unpowered autogyros, which must be towed by a tether to give them forward ground speed or else be tether-anchored to a static anchor in a high-wind situation for kited flight.
Gyrodynes are a form of helicopter, where forward thrust is obtained from a separate propulsion device rather than from tilting the rotor. The definition of a 'gyrodyne' has changed over the years, sometimes including equivalent autogyro designs. The most important characteristic is that in forward flight air does not flow significantly either up or down through the rotor disc but primarily across it. The Heliplane is a similar idea.
Compound rotorcraft have wings which provide some or all of the lift in forward flight. Compound helicopters and compound autogyros have been built, and some forms of gyroplane may be referred to as compound gyroplanes. Tiltrotor aircraft (such as the V-22 Osprey) have their rotors horizontal for vertical flight, and pivot the rotors vertically like a propeller for forward flight. The Coleopter had a cylindrical wing forming a duct around the rotor. On the ground it sat on its tail, and took off and landed vertically like a helicopter. The whole aircraft would then have tilted forward to fly as a propeller-driven fixed-wing aircraft using the duct as a wing (though this transition was never achieved in practice.)
Some rotorcraft have reaction-powered rotors with gas jets at the tips, but most have one or more lift rotors powered from engine-driven shafts

Fixed-wing aircraft

Fixed-wing aircraft

The forerunner of the fixed-wing aircraft is the kite. Whereas a fixed-wing aircraft relies on its forward speed to create airflow over the wings, a kite is tethered to the ground and relies on the wind blowing over its wings to provide lift. Kites were the first kind of aircraft to fly, and were invented in China around 500 BC. Much aerodynamic research was done with kites before test aircraft, wind tunnels and computer modelling programs became available.
The first heavier-than-air craft capable of controlled free flight were gliders. A glider designed by Cayley carried out the first true manned, controlled flight in 1853.
Besides the method of propulsion, fixed-wing aircraft are generally characterized by their wing configuration. The most important wing characteristics are:
Number of wings – Monoplane, biplane, etc.
Wing support – Braced or cantilever, rigid or flexible.
Wing planform – including aspect ratio, angle of sweep and any variations along the span (including the important class of delta wings).
Location of the horizontal stabiliser, if any.
Dihedral angle – positive, zero or negative (anhedral).
A variable geometry aircraft can change its wing configuration during flight.
A flying wing has no fuselage, though it may have small blisters or pods. The opposite of this is a lifting body which has no wings, though it may have small stabilising and control surfaces.
Most fixed-wing aircraft feature a tail unit or empennage incorporating vertical, and often horizontal, stabilising surfaces.
Seaplanes are aircraft that land on water, and they fit into two broad classes: Flying boats are supported on the water by their fuselage. A float plane's fuselage remains clear of the water at all times, the aircraft being supported by two or more floats attached to the fuselage and/or wings. Some examples of both flying boats and float planes are amphibious, being able to take off from and alight on both land and water.
Some people consider wing-in-ground-effect vehicles to be fixed-wing aircraft, others do not. These craft "fly" close to the surface of the ground or water. An example is the Russian ekranoplan (nicknamed the "Caspian Sea Monster"). Man-powered aircraft also rely on ground effect to remain airborne, but this is only because they are so underpowered—the airframe is theoretically capable of flying much higher.

Heavier than air – aerodynes

Heavier than air – aerodynes

Heavier-than-air aircraft must find some way to push air or gas downwards, so that a reaction occurs (by Newton's laws of motion) to push the aircraft upwards. This dynamic movement through the air is the origin of the term aerodyne. There are two ways to produce dynamic upthrust: aerodynamic lift, and powered lift in the form of engine thrust.
Aerodynamic lift is the most common, with fixed-wing aircraft being kept in the air by the forward movement of wings, and rotorcraft by spinning wing-shaped rotors sometimes called rotary wings. A wing is a flat, horizontal surface, usually shaped in cross-section as an aerofoil. To fly, air must flow over the wing and generate lift. A flexible wing is a wing made of fabric or thin sheet material, often stretched over a rigid frame. A kite is tethered to the ground and relies on the speed of the wind over its wings, which may be flexible or rigid, fixed or rotary.
With powered lift, the aircraft directs its engine thrust vertically downwards.
The initialism VTOL (vertical take off and landing) is applied to aircraft that can take off and land vertically. Most are rotorcraft. Others, such as the Hawker Siddeley Harrier, take off and land vertically using powered lift and transfer to aerodynamic lift in steady flight. Similarly, STOL stands for short take off and landing. Some VTOL aircraft often operate in a short take off/vertical landing mode known as STOVL.
A pure rocket is not usually regarded as an aerodyne, because it does not depend on the air for its lift (and can even fly into space); however, many aerodynamic lift vehicles have been powered or assisted by rocket motors. Rocket-powered missiles which obtain aerodynamic lift at very high speed due to airflow over their bodies, are a marginal case.

Classification by method of lift

Lighter than air – aerostats

Aerostats use buoyancy to float in the air in much the same way that ships float on the water. They are characterized by one or more large gasbags or canopies, filled with a relatively low density gas such as helium, hydrogen or hot air, which is less dense than the surrounding air. When the weight of this is added to the weight of the aircraft structure, it adds up to the same weight as the air that the craft displaces.
Small hot air balloons called sky lanterns date back to the 3rd century BC, and were only the second type of aircraft to fly, the first being kites.
Originally, a balloon was any aerostat, while the term airship was used for large, powered aircraft designs – usually fixed-wing[citation needed] – though none had yet been built. The advent of powered balloons, called dirigible balloons, and later of rigid hulls allowing a great increase in size, began to change the way these words were used. Huge powered aerostats, characterized by a rigid outer framework and separate aerodynamic skin surrounding the gas bags, were produced, the Zeppelins being the largest and most famous. There were still no fixed-wing aircraft or non-rigid balloons large enough to be called airships, so "airship" came to be synonymous with these aircraft. Then several accidents, such as the Hindenburg disaster in 1937, led to the demise of these airships. Nowadays a "balloon" is an unpowered aerostat, whilst an "airship" is a powered one.
A powered, steerable aerostat is called a dirigible. Sometimes this term is applied only to non-rigid balloons, and sometimes dirigible balloon is regarded as the definition of an airship (which may then be rigid or non-rigid). Non-rigid dirigibles are characterized by a moderately aerodynamic gasbag with stabilizing fins at the back. These soon became known as blimps. During the Second World War, this shape was widely adopted for tethered balloons; in windy weather, this both reduces the strain on the tether and stabilizes the balloon. The nickname blimp was adopted along with the shape. In modern times any small dirigible or airship is called a blimp, though a blimp may be unpowered as well as powered.

Aircraft

Aircraft

An aircraft is a vehicle which is able to fly by being supported by the air, or in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift (as with balloons, blimps and dirigibles) or by using the dynamic lift of an airfoil (as with vehicles that plane the air with wings in a straight manner, such as airplanes and gliders, or vehicles that generate lift with wings in a rotary manner, such as helicopters or gyrocopters).[1]
Although rockets and missiles also travel through the atmosphere, most are not considered aircraft because they use rocket thrust instead of aerodynamics as the primary means of lift (A cruise missile may be considered to be an aircraft because it relies on a lifting wing).
The human activity which surrounds aircraft is called aviation. Manned aircraft are flown by an onboard pilot. Unmanned aerial vehicles may be remotely controlled or self-controlled by onboard computers. Target drones are an example of UAVs.

Aero planes & Aeroneutical Engineering

AERO PLANES & AERONEUTICAL ENGINEERING

No: 329 SEPTEMBER 20, 1946

Note: The tables referred to in this article have been scanned from originals and may be viewed by clicking on the relevant hyperlink. As graphic files they may take a while to load. We recommend you close the new window each table will generate after viewing. IN RECENT YEARS the advances in aircraft performance have been, very striking. In 1939 speeds of the order of 350 m.p.h. were exceptional, but now they are almost commonplace. Such advances have been made possible by improvements in power unit output, and by aerodynamic refinements, and as a result the designers of aircraft structures have been faced with increasingly difficult problems. They must design their aircraft to withstand very heavy loads, and at the same time they have to bear in, mind the stringent aerodynamic requirements. For example, the thickness of wings must be a minimum and their surfaces should be as smooth as possible. Undoubtedly these requirements will become even more important, and consequently the difficulties of the structural designer will be more acute.

(Above) MODERN WING CONSTRUCTION - A wing panel with "Reduxed" stringers, immediately after removal from the press. They must design their aircraft to withstand very heavy loads, and at the same time they have to bear in, mind the stringent aerodynamic requirements. For example, the thickness of wings must be a minimum and their surfaces should be as smooth as possible. Undoubtedly these requirements will become even more important, and consequently the difficulties of the structural designer will be more acute. The advance from the Mosquito to the Hornet is a good example of how structural designs have developed to meet more exacting conditions. The Mosquito wing spars have wooden tension and compression booms, but this would have been impossible for the Hornet, because of the large cross-section of wood necessary for the tension booms. . As a result the tension booms were made of aluminium-alloy extrusions, while the remainder of the spars were of wood, i.e., the compression booms and the web. The, metal and wood were then welded together so as to form a final spar of remarkably low weight and high strength, and of small depth. One result of the success of this design, and of the testing carried out by the Royal Aircraft Establishment, Farnborough, was the approval given for Redux bonding by M.A.P A D.T.D Specification, No. 775, will shortly be issued to cover the process.

Application to All-metal Aircraft

However, it seems, likely that in the, next few years high performance aircraft will, in a majority of cases, be of all metal construction. The need for smooth, thin wings is greater than ever, and the hitherto normal riveted construction must necessarily come under very severe criticism. Most aircraft skins are literally covered with rivet heads, and consequently determined efforts are being made to diminish their aerodynamic effect, either by polishing operations or by finishing the surface with special paints. Other methods are being tried, including spot welding, but even this leaves a small mark where the electrode makes contact with the skin. This represents one general line of approach to the problem, but there is an alternative which is already, in use on one production aircraft. The de Havilland Dove has fuselage and wing stringers " Reduxed" to the skins. Unlike riveting and spot welding, this does not consist of a large number of small local attachments, but is a bond covering the whole area of contact between stiffener and skin. Hence it achieves two important objectives. It avoids numerous small stress concentrations, and leaves the skin perfectly "clean." Theoretically it seems quite wrong to make a hole in a skin as a first step to attaching a stiffener, and Redux now makes it possible to avoid this.

(Above) A MORE EFFICIENT STRUCTURE - The photograph shows the rear fuselage in a dove in which "Reduxed" stringers are fitted. A comparison between the relative strengths of riveted, spot Welded and Redux-bonded structures, is interesting. Table I compares the results obtained by I. G. Bowen on a large number of tests on riveted joints in Alclad sheet with those obtained with Redux joints. All the joints were 1 in. wide. The strength of the Redux joints is considerably greater than that of the riveted joints, especially when countersunk rivets are used. In Table II will be found a similar comparison between the results of R. Della-Vedowa and M. M. Rockwell, of Lockheeds, on spot-welded joints and Redux joints in 24 S.T. aluminium-alloy sheet.

(Above) STATIC LOAD TESTS - This test is being done on the D.H. Dove with the bonded stringers. When a similar wing of riveted construction is tested, the buckles run through the rivet- holes. Once again the Redux joints are considerably stronger than the others. Nevertheless, these are only small-scale tests and the following results, published by the courtesy of the Aircraft Division of the English Electric Co., Ltd., Preston, are of more direct interest to aircraft designers. Tests were made on flat-ended 16 s.w.g. and 18 s.w.g. panels, each 22 in. long, and of three different aluminium alloys. On the bonded panels rivets were fitted to the end of each stringer. The results are given in Table III. With regard to the results it will be seen that in every case the Redux-bonded panel failed at a higher load than the riveted panel. Further tests on Redux-bonded panels at + 60° C. and -40° C. and under repeated loading at normal temperature all behaved satisfactorily. With the high strength aluminium alloy materials in use at present, wing spars will undergo considerable strains before failure occurs and as a result the panels must be capable of carrying a load not only after the buckling of the skin, but after the initial buckling of the stringers themselves, i.e., after the skin and stringer combination has passed its maximum load. In consequence it is not sufficient to substitute bonding for riveting without first giving a careful consideration to the area of the bond between the stringer and the skin. However tests have shown that, given an adequate area of bond, the Redux will take a considerable load even after buckling.

Full-scale Tests

(Above) TEST TO DESTRUCTION - It can be seen that although the stringers on this Dove wing have fractured (between ribs 6 & 7) the bond is still intact. Finally, we are able to give, by courtesy of the de Havilland Aircraft Co., Ltd., photographs of the full-scale tests on the wing of the Dove. It will be seen from these photographs that "top hat" stringers are used, and it is de Havilland's experience, based upon a large number of unpublished panel tests, that panels with Reduxed "top hat" stringers will develop shear stresses up to 125 per cent. of those developed by exactly similar panels with riveted and spot-welded joints. The results of the full-scale test fully support this conclusion. The appearance of the wing under load is quite different from that of one of riveted construction. In the latter case the buckles all run through the areas of stress concentration, i.e., the rivet holes. In the case of the bonded wing it will be seen that the skin is held firmly along the whole length and the whole width of the stringers. Such a construction is, of course, much stronger than one in which the skin is perforated like a sieve and in which the load is taken on a large number of small areas surrounding the perforations. The wing was subjected to the following series of loadings:- No. of cycles Load cycle (1) 1,200 0 to 2 g. (2) 500 0 to 2.45 g (3) 5 0 to 3.4 g (4) 10,000 0 to 1.5 g (5) 5 0 to 3.86 g (6) 5 0 to 4.37 g (7) Destruction test by static loading to 5.5 g, which is 108% of the design load.

After more than 11,500 stress cycles the wing was in perfect condition, and failure did not occur until after the fully factored load had been passed by an appreciable margin. The failure was an impressive demonstration of the strength and reliability of Redux bonding, because even where the wing skin fractured, only one stringer parted from the skin for a very short length. There can be no doubt whatever that had a conventional riveted structure been tested in a similar way, either the rivet heads would have come off or they might have pulled through the skin. Other Advantages of Redux An improvement in strength is not the only result of using Redux. The skin of the Dove, for example, is in striking contrast to that of most other aircraft because it is so clean. On high-speed aircraft this will become of greater importance in the future. The other advantage is saving in cost. Aircraft riveting is quite an expensive business and Redux is already effecting appreciable economies in aircraft production. In the case of the Dove, Messrs. de Havillands use a large press and sets of stringers are bonded to fuselage and wing skins in sizes up to about 4 ft. by 12 ft. It must be made clear that all the attachments required are made in one operation. When riveting is used it is necessary to jig drill each hole in the stringer and skin as a separate operation, and to countersink each hole in the skin before the actual riveting is carried out. This discussion has mainly dealt with the attaching of stiffeners to skins. There are, however, many other uses for Redux. It is used for constructing the floor of the Vickers-Armstrongs "Viking." In this case a comparatively thin plywood floor is reinforced by top hat stringers. The rolled light alloy sections are first of all bonded to 1 mm. Veneers. Even in a small 6-ft. by 3-ft. press it is possible to bond about 180 ft. in one hour. The veneered sections are then cold glued to the plywood. The floor is then free from any rivet or boltheads and is also strong for its weight. Bonding also makes it possible to attach local reinforcements either to metal or to wood. Good examples of this are to be found in the folding wing attachments of the "Hornet" and the "Mosquito." SIMPLIFIED SPAR CONSTRUCTION - On the left is shown the large box spar assembly on the Mosquito, which makes an interesting comparison with the smaller unit of the Hornet, on the right, with Redux bonding.

DETAIL COMPONENTS - Built up from sheets of Alclad, this provides an example of "Reduxed " local reinforcement. Future Developments There is no doubt whatever that the main difficulty in the development of Redux-bonded structures is its application to doubly curved surfaces. Hitherto flat and singly curved surfaces have caused little difficulty, but at present it is necessary to make up form tools to bond doubly curved panels. At present no other method has been evolved for applying the heat and pressure necessary for bonding. Such tools can, of course, be castings, but even so they tend to be expensive in relation to the numbers of aircraft produced.